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© ABB Group
October 7, 2014
l Slide 1
ABB Protective Relay School Webinar Series
Disclaimer
ABB is pleased to provide you with technical information regarding protective
relays. The material included is not intended to be a complete presentation of
all potential problems and solutions related to this topic. The content is
generic and may not be applicable for circumstances or equipment at any
specific facility. By participating in ABB's web-based Protective Relay School,
you agree that ABB is providing this information to you on an informational
basis only and makes no warranties, representations or guarantees as to the
efficacy or commercial utility of the information for any specific application or
purpose, and ABB is not responsible for any action taken in reliance on the
information contained herein. ABB consultants and service representatives
are available to study specific operations and make recommendations on
improving safety, efficiency and profitability. Contact an ABB sales
representative for further information.
© ABB Group
October 7, 2014
l Slide 2
ABB Protective Relay School Webinar Series
Line distance protection fundamentals
Elmo Price
October 7, 2014
Presenter
Elmo Price received his BSEE from Lamar State College of Technology in
Beaumont, Texas and his MSEE degree in Power Systems Engineering from
the University of Pittsburgh.
Elmo Price
He began his career with Westinghouse in 1970 and worked in many
engineering positions. He also worked as a district engineer located in New
Orleans providing engineering support for Westinghouse power system
products in the South-central U.S.
With the consolidation of Westinghouse into ABB in 1988, Elmo assumed
regional responsibility for product application for the Protective Relay
Division. From 1992 to 2002 he worked in various technical management
positions responsible for product management, product design, application
support and relay schools. From 2002 to 2008 Elmo was a regional
technical manager providing product sales and application support in the
southeastern U.S.
Elmo is currently senior consultant for ABB, a registered professional
engineer and a Life Senior member of the IEEE. He is a member of the IEEE
Power System Relay Committee and the Line Protection Subcommittee,
serving as a contributing member to many working groups. He has two
patents and has authored and presented numerous industry papers.
© ABB Group
October 7, 2014
| Slide 4
Learning objectives
© ABB Group
October 7, 2014
| Slide 5

Line distance measurement methods and characteristics

Apparent impedance of fault loops and differences in
phase and ground measurements

The importance of faulted phase selection

Step distance line protection

Zone acceleration schemes (non-pilot)

Basics of communications assisted schemes
(optional – time permitting)
Distance and impedance relays
~



© ABB Group
October 7, 2014
| Slide 6
ZS
VR
IR
ZL
Uses both voltage and current to determine if a fault
is within the relay’s set zone of protection
Settings based on positive and zero sequence
transmission line impedance
Measures phase and ground fault loops
Distance and impedance relays
Brief History
~

© ABB Group
October 7, 2014
| Slide 7
ZS
VR
IR
ZL
1921 – Voltage restrained time overcurrent was first
form of impedance relaying
•
1929 – Balance beam impedance relay improved
operating speed performance, but was non-directional
•
1950 – Induction cup phase comparator providing mho
distance characteristic
•
1965 – Solid-state implementations
•
1984 – Microprocessor implementations
Impedance relay
Simple balance beam
~
ZS
VR
IR
ZR
X
ZR
Restraint
Torque
VR
R
Operate
Torque
IR*ZR
Reach to balance point = VR/IR = ZR
© ABB Group
October 7, 2014
| Slide 8
Distance relays


Need

Fault levels are higher on high voltage transmission lines

Faults need to be cleared rapidly to avoid instability, and
extensive damage
Advantages






© ABB Group
October 7, 2014
| Slide 9
The impedance zone has a fixed impedance reach
Greater Instantaneous trip coverage with security
Greater sensitivity
Easier setting calculations and coordination
Fixed zone of protection that are relatively independent of system
changes
Higher independence of load
Distance relay application
ZR
G
ZG
H
ZH
ZL
Relay
Relay
ZH
X
H
Impedance
Plane
ZR
Operating
Characteristic
ZL
R
G
ZG
© ABB Group
October 7, 2014
| Slide 10
Distance relay characteristics
Impedance
ZH
X
No operation region
ZR
Operate
H
ZL
MTA
R
G
32 (Directional unit)
© ABB Group
October 7, 2014
| Slide 11
Distance relay characteristics
Mho distance, self (fault voltage) polarized
ZH
X
No Operation Region
ZR
H
ZL
Operate
MTA
G
© ABB Group
October 7, 2014
| Slide 12
R
Distance relay characteristics
Mho distance, (healthy) voltage polarized
ZH
X
•
ZR
No Operation Region
Typical polarizing
Quantities
H
ZL
Operate
R
ZG
© ABB Group
October 7, 2014
| Slide 13
G
•
Cross
•
Positive Sequence
•
Memory
Distance relay characteristics
Offset mho distance
ZH
X
No operation region
ZR
H
ZL
Operate
G
Close-in faults
© ABB Group
October 7, 2014
| Slide 14
MTA
R
32 (Directional unit)
Distance relay characteristics
Reactance
ZH
X
No operation region
XR
ZR
Operate
ZL
MTA
G
- XR
© ABB Group
October 7, 2014
| Slide 15
H
Load
supervision
R
R
32 (Directional unit)
Distance relay characteristics
Quadrilateral
X
No operation region
ZH
XR ZR
ZL
H
Good
resistance
coverage
Operate
MTA
G
MTA
R
RR
32 (Directional unit)
© ABB Group
October 7, 2014
| Slide 16
Distance relay characteristics
Switched zone quadrilateral
No operation region
X
Zone-3
Operate
Zone-2
Zone-1
© ABB Group
October 7, 2014
| Slide 17
R
Distance relay characteristics
Mho distance with switched reactance
X
No operation region
Zone-3
Zone-2
Zone-1
Operate
© ABB Group
October 7, 2014
| Slide 18
R
Distance relay characteristics
Lenticular
No operation region
ZH
X
H
MTA
G
© ABB Group
October 7, 2014
| Slide 19
Multi-phase
faults
R
Phase comparators
S1
S2
PHASE
COMPARATOR
S1
Compares the phase
angle of two phasor
quantities to determine
operation
© ABB Group
October 7, 2014
| Slide 20
1/0
S2
OPERATE
RESTRAIN
Apply
operating
torque
Apply
opening
torque
Distance relay characteristics
KD-10 cylinder unit (comparator) and compensator
IA
VA
IB
X
CYLINDER
UNIT
ZR
S1
XZY
IC
VC
S2
VB
© ABB Group
October 7, 2014
| Slide 21
FZY
Z
ZR
COMPENSATOR
Y
Phase-to-phase unit
FXY
Distance relay characteristics
KD-10 cylinder unit
Compensator
IA - I B
VAG
VXY = VAB - (IA - IB)ZR
(IA - IB)ZR
X
IC - IB
FXY
VXY
VCG
Z
VCB
(IC - IB)ZR
VZY
Y
VBG
© ABB Group
October 7, 2014
| Slide 22
Cylinder unit
VZY = VCB - (IC - IB)ZR
FZY
Trips when
VXY leads VZY
XZY
sequence
Distance relay characteristics
Mho distance phase comparator principle
Generic single phase self polarized without zero sequence compensation
IX
IX
IZC – IZ
IZC
IZC - IZ
IZC
ß
IZ
IR
V
(a) Self (faulted phase) Polarized
ZC = impedance reach setting
Z = fault impedance
Vf = fault voltage at relay
I = fault current
© ABB Group
| Slide 23
ß > 90°
S2
IZ
October 7, 2014
ß < 90°
IR
V
(b) Internal and External Fault
S1  V f  IZ
S 2  IZ C  V f  IZ C  IZ
Trip b < 90O
S1
Distance relay characteristics
Mho distance phase comparator – cross polarized
IX
IZC - IZ
IZC
Generic single phase (healthy) voltage
polarized without zero sequence
compensation
IZ
V
I(Z+ZS)
IR
IZS
VS
Z+ZS = fault impedance from source
VS = source voltage
© ABB Group
October 7, 2014
| Slide 24
S1  I ( Z  Z S );VBC , V1 , VMem
S 2  IZ C  IZ
Distance relay characteristics
Mho distance phase comparators
VOP
VPOL
Zc*IXY - VXY
jVXY
XY = AB, BC, CA
Zc = setting
Zc*IXY - VXY
VZ
XY = AB, BC, CA
Z = C, A, B
Zc = setting
VAB –
(IA – IB)Zc
Zc = setting
VCB –
(IC – IB)Zc
 Three units required for phase-to-phase
and three-phase
 Self Polarizing
 No expansion
 Requires directional unit supervision
 Requires memory for zero voltage faults
 VOP leads VPOL
 Three units required for phase-to-phase
and three-phase
 Cross Polarizing
 Source Impedance expansion
 Requires directional unit supervision
 Requires memory for zero voltage faults
 VOP leads VPOL
 Single unit required for phase-to-phase
(AB, BC, CA)
 Separate unit required for three-phase
faults
 Source Impedance expansion
 VOP leads VPOL
Positive Sequence Polarizing, VPOL == sub jVZY with VX1
© ABB Group
October 7, 2014
Comments
| Slide 25
Distance relay characteristics
Mho distance phase comparators
Comments
VOP
VPOL
VXG –
Zc*(IX + K0I0)
VZY
X = A, B, C
YZ = BC, CA, AB
I0 = 1/3(IA+IB+IC)
K0=(Z0 - Z1)/Z1
VXG –
Zc*(IX + KNIR)
jVZY
X = A, B, C
YZ = BC, CA, AB
IR = IA+IB+IC
KN = (Z0 - Z1)/3Z1
 Three units required for phase-toground (A, B, C)
 zero sequence (I 0)compensation
 Cross Polarizing
 Source Impedance expansion
 Requires directional unit
supervision
 VOP leads VPOL
 Three units required for phase-toground (A, B, C)
 Residual ground (I r=3I0)
compensation
 Cross Polarizing
 Source Impedance expansion
 Requires directional unit
supervision
 VOP leads VPOL
Positive sequence polarizing, VPOL == sub jVZY with VX1
© ABB Group
October 7, 2014
| Slide 26
Quadrilateral characteristics
Reactance Lines (current polarization)
S1 = IZC - V = (XC - Z)I
q
S2 = VPOL = XCI
XC - Z
XC
Only the forward reach line can be defined,
therefore, it must be directionally supervised
S1
X
ZC
Z
S2
q
Z
RC
RF
-XC
q
Operate q < ± 90O

© ABB Group
October 7, 2014
| Slide 27
I2 used for load compensation
R
Quadrilateral characteristics
Resistance (current polarized)
X
S1 = IRCF - V = (RCF - Z)I
S2 = VPOL = RCFI
Z
RCF
S1
q
S2
RCF - Z
q
RCF
Z
R
Operate q < ± 90O
© ABB Group
October 7, 2014
| Slide 28
Distance relay characteristics
Reference
E. Price, T. Einarsson, “Complementary Approach for
Reliable High Speed Transmission Line Protection,” 62nd
Annual Georgia Tech Protective Relaying Conference,
Atlanta, Georgia, 2008.
© ABB Group
October 7, 2014
| Slide 29
Apparent impedance of fault loops
6 fault loops measured for
each zone
AG
BG
CG
Fault Types
• Phase-to-ground
• Phase-to-phase
AB
CA
• Two phase-to-ground
• Three phase
BC
© ABB Group
October 7, 2014
| Slide 30
Apparent impedance of fault loops
Three phase
X
ZL1
ZR1
IN = 0
ZLN
MTA
R
Relay Phase Impedance
Characteristic
Apparent impedance
phase)
VA= IA ZL1
Z3P = ZL1 =VA/IA
© ABB Group
October 7, 2014
| Slide 31
(per
ZL1
ZL1
Fault applied on line at ZL1
Phase reach is set in terms of
positive sequence impedance, ZL1
Apparent impedance of fault loops
Phase-to-phase
ZL1
X
ZL1
MTAP
R
Relay Phase-to-phase
impedance characteristic
Apparent impedance, ZPP
VAB = (IA - IB ) ZL1 = 2IA ZL1
ZPP =ZL1 = VAB/(IA - IB ) = (VA - VB )/(IA - IB )
Phase reach is set in terms of positive sequence impedance, ZL1
© ABB Group
October 7, 2014
| Slide 32
ZLN
ZL1
ZL1
Apparent impedance of fault loops
Phase-to-ground
X Z
L1
ZG = ZL1 + ZLN
ZL1
MTAP
ZLN
MTAG
ZL1
R
Relay Phase-to-ground
impedance characteristic
Apparent impedance
(no load IA = 3I0 )
VA = IA ZL1 + 3I0ZLN = IA (ZL1 + ZLN)
ZG = VA /IA = (ZL1 + ZLN)
© ABB Group
October 7, 2014
| Slide 33
MTAG = Argument ( ZL1 + ZLN )
ZL1
Apparent impedance of fault loops
Phase-to-ground
Apparent impedance
X Z
L1
MTAP
Arg(1+KN)
ZG = (ZL1 + ZLN)
ZLN = (ZL0 - ZL1) / 3
ZG = (2ZL1 + ZL0) / 3 (ground loop)
MTAG
R
Relay Phase-to-ground
impedance characteristic
ZL1 with residual 3I0 compensation
ZG = ZL1 ( 2 + ZL0 / ZL1) / 3
ZG = ZL1 ( 2 + 1 + ZL0 / ZL1 - 1 ) / 3
ZG = ZL1(1 + KN); KN = (ZL0 - ZL1)/3ZL1
MTAG = Arg( ZG)
© ABB Group
October 7, 2014
| Slide 34
Apparent impedance of fault loops
Phase-to-ground
Two Factors used by different relays and manufacturers
Residual [neutral] current compensation
KN compensates for 3I0
VA  Z
KN 
K0 compensates for I0
Ground reach is set in terms of ZL1 and KN:
© ABB Group
October 7, 2014
| Slide 35
K0 
ZL0 - ZL1  
I  3I

3ZL1  


0


ZL0 - ZL1
3ZL1
VA  Z
Zero sequence current compensation


L1  A




L1  A



ZL0

I I
- 1 

ZL1



0


ZL0
-1
ZL1
ZG = ZL1(1 + KN)
Faulted phase selection
Release or identify correct
impedance loop
A-B
A-G
B-C
B-G
C-A
C-G
6 fault loops measured in each
zone
© ABB Group
October 7, 2014
| Slide 36

Single pole trip

Event recording

Fault location
Faulted phase selection
Issues
Multiple impedance loop operations
for a fault event
A-B
A-G
© ABB Group
October 7, 2014
| Slide 37
B-C
B-G
C-A
C-G
•
Common phases of a fault loop
•
Magnitude of fault quantities
•
Load
•
Fault resistance
Faulted phase selection
Issues
The FF unit may operate for close-in reverse FF, FFG, or
FG faults
The FF unit may operate for close-in forward FG faults
The FG units may operate for close-in reverse FG faults
The FF unit of a non-faulted loop may operate for FFG
faults with high fault resistance






e.g. CA unit for a BCG fault
The CA operation will occur with the expected BC operation
giving the appearance of a three phase fault.
These issues are resolved with directional and/or sequence current supervision.
© ABB Group
October 7, 2014
| Slide 38
Faulted phase selection
Issues

The FG unit of the leading phase will overreach for
forward external FFG faults with any measurable fault
resistance


e.g. BG unit for a BCG fault
The FG unit of the lagging phase will underreach for
forward internal FFG faults near the reach setting with any
measurable fault resistance


e.g. CG unit for a BCG fault
This is generally of no consequence
These issues are the result of FFG faults and must be resolved by accurate phase
selection.
© ABB Group
October 7, 2014
| Slide 39
Faulted phase selection
Response of BG, CG and BC units to BCG fault
5
2
Fault Location in PU of Zone Reach Setting, Zc
SIRz
3
1.5
Error Zone of FG
units for FFG faults
B
BG is operated
1
0.5
Overreaching BG Units
1
BC Unit
Underreaching CG Units
Operates f or all
parameters at 1.0
A
0.5
0.5
1
CG is operated
3
5
0
0
October 7, 2014
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Per Unit Fault Resistance, Rg
© ABB Group
| Slide 40
0.08
0.09
0.1
Faulted phase selection
Reference
E. Price, T. Einarsson, “The Performance of Faulted phase
Selectors used in Transmission Line Applications,” 62nd
Annual Georgia Tech Protective Relaying Conference,
Atlanta, Georgia, 2008.
© ABB Group
October 7, 2014
| Slide 41
Application
Location of cts and vts
© ABB Group
October 7, 2014
| Slide 42

Reach of a distance relay is measured from the
location of the voltage transformer

Directional sensing occurs from the location of the
current transformer

In most applications vts and cts are usually at same
location (no measurable impedance between them)

Their location should always be considered
especially for applications with transmission lines
terminated with transformers
Application
Step distance protection
T3
T2
T1
Z3
Z2
Z1
G
H
Z1
Z3



© ABB Group
October 7, 2014
| Slide 43
Z2
T1
T2
T3
Zone 1 set for 80 - 90 % of line impedance
Zone 2 set for 100% of line plus 25 - 50% of shortest adjacent
line from remote bus
Zone 3 set for 100% of both lines plus 25% of adjacent line
off remote bus
Step distance protection
Zone 1
T3
T2
T1
Z3
Z2
Z1
G
H
Z1
Z3



© ABB Group
October 7, 2014
Z2
T1
T2
T3
Do not want Zone 1 to reach beyond remote bus
10 to 20% is safety factor
Inaccuracies
 Relays
 Current and potential transformers
 Line impedances
| Slide 44
Step distance protection
Zone 2
T3
T2
T1
Z3
Z2
Z1
G
H
Z1
Z3



© ABB Group
October 7, 2014

| Slide 45
Z2
T1
T2
T3
H
Z1
R
Operates through a timer (T2)
Timer set for Coordination Time Interval (CTI) that allows
remote relay zone 1 [Z1] and breaker [at H] to operate with
margin before zone 2 [Z2] relay
Z2 at G must overreach the remote bus H, but should not
overreach the closest far bus at R
Z2 at G is remote backup to Z1 at H
Step distance protection
Zone 3
T3
T2
T1
Z3
Z2
G
H
Z1
Z3



© ABB Group
October 7, 2014
| Slide 46
Z2
R
Z1
H
Z1
Z2
T1
T2
T3
Operates through a timer (T3)
Timer set for Coordination Time Interval (CTI) that allows
remote relay zone 2 [Z2] and breakers [at H and R] to
operate with margin before the zone 3 [Z3] relay
Z3 at G is also remote backup to Z1 and Z2 at H
Step distance protection
Zone 3
T2
T3
Z3
T1
Z1
R
Z2
Z1
G
H
Z1
Z2


© ABB Group
| Slide 47
T1
T2
Zone 3 relay [Z3] may be applied looking reverse for pilot
system logic with no timer
Zone 3 relay [Z3] may be applied looking reverse for reverse
[backup] bus protection

October 7, 2014
T3
Timer set to allows reverse zone 1 [Z1] relay and breaker [at G]
to operate with margin before zone 3 [Z3] relay
Step distance protection
Operating time profile
Z3
Z2
Z1
T3
T2
21/67 (Impedance controlled directional TOC)
Z2
Z2
Z1
© ABB Group
October 7, 2014
| Slide 48
Z1
Step distance protection
Infeed [from remote bus]
Z2
Z1
G
IG
IIN




© ABB Group
October 7, 2014
| Slide 49
Reduces the apparent reach measured by distance relays
Depends on the ratio between current going through relay
(IG) and current from infeed (IIN)
Usually not a factor on Zone 1 [Z1] relay unless tapped line
[or appreciable fault resistance for ground faults]
Zone 2 may underreach remote bus
Step distance protection
Infeed [from remote bus]
Z2
VG
ZG
G
G
IG
IIN
ZH
IG+ IIN
H
With Zero voltage fault and Z2 = ZG + ZH
VG = IGZG + ( IG + IIN ) ZH
ZA (Apparent) = VG / IG
ZA = ZG + (1 + IIN/IG) ZH
ZA = ZG + ZH + (IIN/IG)ZH (Increase in Apparent Impedance)
Z2 must be set to overreach bus H for infeed at bus H
and not overreach bus K for no infeed at bus H
© ABB Group
October 7, 2014
| Slide 50
K
Step distance protection
Outfeed
Z1 = 2.5 W
G
1W
2W
2a
1a
1W
1a
1W
1a
Usually associated with three terminal line applications and paralleling of line segment
Example:
VG = 2(1) + 2(1 ) = 4
ZG (Apparent) = VG / IG
ZG = 4/2 = 2 W
Z1 will overreach and see the fault
© ABB Group
October 7, 2014
| Slide 51
Step distance protection
Tapped transformers and loads
m
mZL
G
IG
ZT
(1-m)ZL
IH
IG + IH
VG = IGmZL + ( IG + IH ) ZT
ZG (Apparent) = VG / IG
ZG = mZL + (1 + IH/IG) ZT
ZG = mZL + ZT + IH/IGZT (Increase in apparent impedance)
Apparent impedance will always be larger than impedance to fault
© ABB Group
October 7, 2014
| Slide 52
Step distance protection
Lines terminated into transformers
ZT
IL
ZL
IH
VL
VH
IH and VH preferred to provide line protection
Use of VL and/or IL affects measured impedance and requires
ct and/or vt ratio adjustment
Transformer should always be protected separately



Reference
E. Price, R. Hedding, “Protecting Transmission Lines Terminated into
Transformers,” 63nd Annual Georgia Tech Protective Relaying
Conference, Atlanta, Georgia, 2009.
© ABB Group
October 7, 2014
| Slide 53
Source impedance ratio



Ratio of source impedance to the line impedance
SIR to the relay is the ratio of source impedance to
the zone impedance setting
The higher the SIR the more complex the line
protection with zone 1
 Measurement errors are more pronounced




© ABB Group
October 7, 2014
| Slide 54
Current and or voltage transformer error
CVT transients
Zone-1 may not be recommended in many
applications
Current differential protection preferred
Source impedance ratio
Recommended applications



Short Line

Current Differential

Phase Comparison

Pilot (POTT, DCB)
Medium Line

Above

Step Distance
Long Line


SIR > 4.0
4.0 > SIR > 0.5
0.5 > SIR
Above
Step Distance
IEEE Guide for Protective Relay Applications to
Transmission Lines - IEEE Std C37.113-1999
© ABB Group
October 7, 2014
| Slide 55
Non-pilot applications
Zone 1 extension
Z1
Z1
Z1
A




© ABB Group
October 7, 2014
| Slide 56
B
C
Z1
F
D
Z1 reach is initially set to overreach remote bus
Circuit breakers controlled by relays A, C, & D trip for a fault
at F
Z1 reach is reduced to not overreach remote bus
High-speed reclose
Non-pilot applications
Zone 1 extension
Z2
Z1
Z1
Z1
Z1
A



© ABB Group
| Slide 57
C
F
D
After high-speed reclose

October 7, 2014
B
Circuit breaker controlled by relay C trips instantaneously
Circuit breaker controlled by relay D trips time-delayed
Circuit breaker controlled by relay A does not trip
Non-pilot applications
Load loss trip
Z2
Z2
Z1
Z1
A





© ABB Group
| Slide 58
F
B
Unbalanced fault occurs at F
Breaker controlled by relay B trips instantaneously by Z1
Balanced load current, IL, is interrupted
LLT Logic at A

October 7, 2014
IL
Detects loss of balanced (load) current and bypasses Z2
timer to trip
Does not operate for three-phase fault
Switch onto fault logic
ZSOTF
I
CLOSING
A


Breaker position
Dead line logic
When breaker controlled by relay A closes SOTF asserts
when:


I and Not V, and/or
ZSOTF operates

© ABB Group
October 7, 2014
| Slide 59
B
Logic determines breaker has been open awhile and sets
SOTF logic (aka: CIFT, SOFT)


V
OPEN
Set ZSOTF offset, overreaching line and below minimum load impedance
Stub bus protection logic
© ABB Group
October 7, 2014
| Slide 60
Pilot relaying schemes
Communication assisted schemes
Goal - High speed simultaneous tripping of all line
terminals for internal line faults
STATION C
A
STATION D
X
B
P&C
STATION E
P&C
C
P&C
© ABB Group
October 7, 2014
| Slide 61
Pilot relaying schemes
Communication assisted schemes
Goal - High speed simultaneous tripping of all line
terminals for internal line faults
STATION C
A
STATION D
X
B
P&C
STATION E
P&C
C
COMMUNICATIONS
P&C
Requires reliable high-speed communications
between line terminals.
© ABB Group
October 7, 2014
| Slide 62
Pilot Communications
 Power Line Carrier (PLC)

The communication signal is coupled to the transmission line being protected
requiring additional substation equipment

Line traps

Line tuners

Coupling capacitors

On/Off Keying, Frequency Shift Keying (FSK)

Generally more available and economical than other forms of pilot
communications

Communication issues tend to occur when reliable communications is need
most – during the fault

DCB (On/Off) and DCUB (FSK) developed specifically for PLC
63
Pilot Communications
 Non Power Line Carrier
64

The communication signal is routed separately from
the transmission line conductor

Audio tone – FSK over voice (telephone, microwave)

Digital – most reliable, particularly with fiber optics,
direct connected or multiplexed
Directional Comparison
Directional Comparison relaying determines the fault direction at each line
terminal and compares the results to determine the fault to be internal or
external to the protected line.
FWD Element (FP-A)à
INTERNAL
FAULT
FINT
A
ßFWD Element (FP-B)
STATION C
FWD Element (FP-A)à
EXTERNAL
FAULT
A
STATION C
65
B
STATION D
STATION D
B
FEXT
REV Element (RP-B)à
Distance Protection
Directional Comparison Schemes
Non PLC Channels

DUTT* – Direct-underreaching transfer trip

POTT – permissive-overreaching transfer trip

PUTT – permissive-underreaching transfer trip
PLC

DCB – directional comparison blocking

DCUB – directional comparison unblocking
* Although there is no directional comparison between terminals this scheme is
usually considered with directional comparison schemes.
66
DUTT – Direct-underreaching Transfer Trip
STATION D
STATION C
A
B
FINT
21-1
21-1
Must
Overlap
Comm
Tx
Rx
Rx [f1 from B]
21-1 (A)
TRIP A
OR
Tx [f1 to TRIP B]
 Also known as an “Intertrip” scheme
67
Tx
Rx
f1
Comm
Rx [f1 from A]
21-1 (B)
Underreaching
Distance Relay
OR
TRIP B
Tx [f1 to TRIP A]
DUTT – Direct-underreaching Transfer Trip
 Advantages

Fast method for clearing end zone faults

Single communications channel
 Disadvantages




68
Cannot protect full line if one terminal is open or has
weak infeed
Requires ground distance relays for accurate reach on
ground faults (no overcurrent)
Subject to 21-1 overreaching issues (e.g. ccvt
transients)
Spurious communication channel noise may cause
undesired trip (secure channel desired – FSK, digital)
PUTT – Permissive-underreaching Transfer Trip
STATION D
STATION C
A
B
Must
Overlap
21-1
FINT
21-1
Overreaching
Distance Relay
Underreaching
Distance Relay
21-2
21-2
Comm
Tx
Rx
Rx [f1 from B]
21-2 (A)
21-1 (A)
AND
Tx
Rx
f1
TRIP A
Tx [to B]
Comm
Rx [f1 from A]
21-2 (B)
21-1 (B)
Rx signal should have a minimum receive time to allow operation of 21-2.
69
TRIP B
AND
Tx [f1 to A]
PUTT – Permissive-underreaching Transfer Trip
 Advantages

More secure than DUTT requiring a 21-2 operation for
permission to trip

Single communications channel
 Disadvantages
70

Cannot protect full line if one terminal is open or has
weak infeed

Requires ground distance relays for accurate reach on
ground faults (no overcurrent)
POTT – Permissive-overreaching Transfer Trip
STATION D
STATION C
A
B
FINT
FP-A
Overreaching Distance
FP-B and OC Relays:
21-2, 21N-2, 67N
Comm
Tx
Rx
Rx [f2 from B]
FP-A
AND
f1
TRIP A
f2
Tx
Rx
Comm
Rx [f1 from A]
FP-B
AND
Tx [f1 to B]
Rx signal should have a minimum receive time to allow operation of 21-2.
71
TRIP B
Tx [f2 to A]
POTT – Permissive-overreaching Transfer Trip
 Advantages

More dependable than PUTT because it sees all line
faults.

Open terminal and weak-end infeed logic can be applied.

Forward and reverse ground directional overcurrent
relays may be applied for greater sensitivity to high
resistance ground faults
 Disadvantages

Requires a duplex communications channel (separate
frequency/signal for each direction)

Will not trip for internal fault with loss of channel (but
usually applied with a zone-1/2 step-distance
relay)
72
Directional Comparison
Blocking (DCB) and Unblocking (DCUB)
 DCB and DCUB schemes are specifically intended to be used with systems where
communications is less secure (likely to be lost) during line fault conditions
 Power-line carrier – signal
communications is on same
conductor that you are protecting
STATION C
STATION D
A
Transmission Line
B
Power Line
Carrier
Channel
Relay
73
Relay
The PLC Channel
Station A Bus
Signal:
30 to 500 kHz
1 to 100 Watts
(7 to 70 V rms)
Line Trap
Fault
2
1
Signal Path
Switchyard
Control
House
Protective
Relay
System
T
Relay PT
inputs
Coaxial Cable
Coupling Capacitor
Voltage
Transformer (ccvt)
H
R
Drain
Coil
Line
Tuner
DCUB – Directional Comparison Unblocking
fB1 and fB2 are continuous block signals until a fault is detected and
the frequency is shifted to the unblock (trip) f1 and/or f2.
75
DCUB – Directional Comparison Unblocking
 Advantages

Very secure at it requires receipt of Unblock signal for
tripping.

Has logic to handle loss of channel during faults.

Open terminal and weak-end infeed logic can be applied.

Forward and reverse ground directional overcurrent
relays may be applied for greater sensitivity to high
resistance ground faults

Security logic for loss of channel (carrier holes) only
delays trip during loss of channel
 Disadvantages

76
Requires a duplex communications channel (separate trip
and guard frequencies for each direction)
DCB – Directional Comparison Blocking
77
DCB – Directional Comparison Blocking
 Advantages

Very dependable – does not depend on channel for tripping for internal
faults

Open terminal and weak-end infeed are handled by scheme

Forward and reverse ground directional overcurrent relays may be applied
for greater sensitivity to high resistance ground faults

Low cost communications channel – single frequency channel On/Off PLC
 Disadvantages

Not as secure – tends to overtrip for slow channel or loss of channel

Security logic for carrier holes may be required – slows tripping.

Channel is normally off so periodic checking is required
78
References
© ABB Group
October 7, 2014
| Slide 79
1.
IEEE Guide for protective Relay Applications to
Transmission Lines, IEEE Std. C37-113, 1999.
2.
W. A. Elmore, Protective Relaying: Theory and
Application, Marcel Decker, Inc., New York,1994.
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•
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Thank you for your participation
Shortly, you will receive a link to an archive of this presentation.
To view a schedule of remaining webinars in this series, or for more
information on ABB’s protection and control solutions, visit:
www.abb.com/relion
© ABB Group
October 7, 2014
| Slide 82